How to Install a Basement Dehumidifier

This project shows how to install a basement dehumidifier and drain the condensate water to the outdoors for continuous operation. A dehumidifier extracts moisture from the air and is a great way to lower the humidity in a basement. This makes the air fresher and reduces the chance for mold. I wanted a dehumidifier to eliminate any chance of rust on the tools in my basement workshop. The humidity in the basement ranged from around 40% in dry weather up to 70% in damp weather. I wanted to limit the humidity to around 50%, which is on the dry side. The question I faced is “What to do with the water?”.

How to Install a Basement Dehumidifier

Room size humidifiers have a condensate bucket that must be emptied by hand. A float switch turns off the humidifier when the bucket is full to prevent overflows. Many humidifiers also provide a threaded spigot to connect a water hose for drainage, assuming you have a floor drain or sump pump to take away the water. A daily routine of checking and emptying the condensate bucket wasn’t going to happen. I’ve got better things to do. My basement doesn’t have a floor drain or sump pump, so draining the unit with a water hose wasn’t an option… then I had an idea.

The solution was to elevate the dehumidifier above grade level and use PVC plastic pipe to drain away the water. This is possible because my house sits on a hillside and the basement is above ground on three sides.

One (1) 1/2 inch PVC to garden hose bibcock adapter (available at Home Depot or Lowes).

Basement Dehumidifier Installation

Pick a location several feet above the exterior ground level that is free of electrical, plumbing and natural gas lines. I used the natural gas pipe entrance to locate and mark a position on the exterior and interior walls for the 1/2 inch PVC drain pipe.

Cut the 14 x 17 inch plywood shelf to rest the humidifier upon from a scrap sheet of plywood. I used 5/8 inch plywood as it is strong with enough thickness for the wood screws to hold fast.

Using a carpenters level, mark the level line on the 2×4 wall studs for the top of the shelf, at or slightly above the height where the drain line will penetrate the wall. Attach the shelf brackets to the 2×4 wall studs with the wood screws, the top of the brackets even with the level line.

Attach the plywood shelf to the brackets with wood screws driven from the bottom of the shelf (screws are pointing upward).

Drill a 1/4 inch pilot hole in the basement wall at the location marked for the drain line.

With a 1/2 inch drill bit, enlarge the pilot hole to 1/2 inch. You may need a masonry drill bit if the wall is construction is stucco, brick, cinder block or poured concrete.

Remove all wheels or casters from the humidifier.

Center the humidifier on the plywood shelf.

Using a tape measure, cut and dry fit (no glue) the PVC to garden hose adapter, pipe sections and 90 degree elbows. Trim and adjust the plumbing as needed.

When your satisfied with the PVC plumbing connections, glue the sections together. PVC is very easy and fast to glue. Swab the mating ends with purple cleaner, swab on some glue and press together. The bond is permanent in a minute.

Caulk the the PVC pipe where it exits the wall to provide a water tight seal.

The following photos will clarify the layout and fittings.

The PVC to brass garden hose adapter and other pipe fittings are shown in the photo below. The humidifier drain bucket has been removed to view the interior.

Basement Dehumidifier Condensate Drain PVC Pipe Fittings

The finished PVC drain pipe connections.

Basement Dehumidifier: Shelf Mount and PVC Drain Pipe

The PVC drain pipe exit through the exterior wall. The natural gas pipe was used to locate and mark the PVC exit at a suitable location above ground level.

Basement Dehumidifier: Outdoor PVC Drain Pipe

The PVC pipe just lays on top of the ground, covered with pine straw as shown in this photo. It’s important to run the line away from the foundation because a persistent wet spot can invite termites.

Basement Dehumidifier PVC Drain Pipe

Tip: Do not glue the vertical PVC pipe run into the 90 degree elbow at the wall exit. The dry fit connection is water tight (because there is no pressure in the line) and allows freedom of movement for the drain end to avoid saturating the ground. When I mow the yard, I swing the drain end of the pipe 3 feet or so to a new spot. Take care to keep the pipe drain at least 6 feet or more from the foundation wall to discourage termites.

An improvement would be to extend and bury the PVC pipe several inches under the sod to a permanent drainage position 20 feet or so from the foundation. I didn’t bury the line due to phone, electrical and CATV lines in the immediate area.

The dehumidifier shouldn’t be placed inside the closet because it will just recycle the air within the closet. The humidifier pulls air in from the front and blows it out the top, creating a closed loop inside the closet.

So, a 12×12 door vent is practically the same as a solid door. A louvered door won’t do much better because the exhaust air will hit the closet ceiling and spill down the walls/doors only to be pulled into the dehumidifier again.

How about locating the dehumidifier outside the closet and placing a folding room divider in front of the unit?

Thanks for the quick reply Bob. That could work. Now I have another question. The basement has a living space, two small bedrooms and a full bath. Do I need more than a 70 pint dehumidifier? 600-700 sq ft.

Also, do you know how much louder the optional pump will make the unit? Leaning towards upgrading to the pump option and putting the unit on the floor. Instead of high up. Thanks again.

A 70 pint per 24 hour capacity will handle > 3500 square feet of floor space according to this Lowes Buying Guide. However the Hisense DH-70KP1SDLE 70 pint dehumidifier with pump data sheet states a much more conservative “for spaces up to 1500 square feet”. Still more than sufficient for your 600 to 700 sq. ft. living space.

> Also, do you know how much louder the optional pump will make the unit? I don’t know for certain, but you’ll probably hear a whirring sound when the pump activates. As a rough comparison my air conditioner condensate pump is not loud, but it might wake you up if you’re a light sleeper. The dehumidifier fan and compressor motor noise level is about 54 decibels which will probably be louder than the pump.

Carefully read the warranty for whichever dehumidifier you decide to buy, save your receipt and register your product. It’ll run constantly in the high humidity basement and in my experience *always* breaks before the warranty expires, which typically covers 1 year full and 3 or 5 years on the refrigeration system (compressor/fan). I’m on my 3rd warranty replacement in a row. Two failed during the 1st year, the compressor failed on the 3rd unit after 2 years.

An outdoor drain line will freeze and clog during the winter in a cold climate. You’d need to empty the condensate indoors by one of the following options: * Direct the drain tube to a basement floor drain. * If you have a clothes washer in the basement, put the drain tube in the washer sewer drain. * Install a condensate pump and connect the drain tube to an overhead sewer pipe.

There are dehumidifiers with a built-in condensate pump (ejector pump) but the specifications often don’t say how high it will lift the water. In my experience dehumidifiers fail after one or two years (I’m on my 3rd consecutive warranty replacement) where a quality condensate pump will last 10 years. The disadvantage of a separate pump is the risk of a pump failure and inability to automatically turnoff the dehumidifier to prevent flooding.

The simple flood prevention solution is to place the pump in a pan on the floor and install a water leak sensor. If the pump fails the dehumidifier will continue to operate and the pump reservoir will overflow into the pan triggering the leak sensor audible alarm.

A more advanced flood prevention approach is to wire in a 120VAC dry contact relay between the condensate pump and the dehumidifier. This is how it works for a central air conditioning system so the condensate pump float switch will turn off the AC if the reservoir is full. This is an advanced project best left to a licensed electrician.

Hi Bob! Thank you for your great article! I’ve been searching to no avail and am hoping you can answer my question.

My home is a simple 1950s raised ranch with poured concrete walls in the basement. The upper level is 925sf and the basement is the same sq ft broken into 1/3 basement living area, 1/3 laundry/utility space, 1/3 single car garage. I have a floor drain in the laundry/utility room so I will easily be able to drain the humidifier. So my question is – if I am able to directly drain the humidifier, what size do I need for my space? Do I get the size for my space or can I go smaller since I don’t have to manually drain?

Additional info – my poured concrete basement walls (the sides which are deeper than the garage side) will often sweat in the winter time – will this help?

The Association of Home Appliance Manufacturers (AHAM) dehumidifier sizing table suggests a 23 pints per 24 hours unit should be sufficient for an extremely wet 925 square feet basement.

However a single unit in the laundry room may not be very effective for the basement living area and single car garage due to limited air exchange between the various rooms. The laundry room would be dry but the living area not so much. Better to install at least two units – one in the laundry room and another unit in the living area. You’ll need to empty dehumidifier bucket by hand in the living area.

Basement garages normally aren’t insulated or heated. If the garage door is rarely opened there is very little air exchange and a 3rd dehumidifier would be reasonable. Set the garage dehumidifier on a 3 feet high platform and run a drain hose through the wall to the laundry room drain so it won’t freeze in the winter.

There is a furnace/HVAC unit in my basement which already has a pump and small vinyl tube running out the foundation to the outside. I am in Rhode Island, with some cold weather. Might I expect the same problem you mentioned in a prior post, freezing during the winter months, and backups, were I to T into the tubing? Or does this type of unit operate all season, with condensate to remove in the winter months? If I only piggybacked onto the furnace tube in the summer, are there other considerations, e.g., backing up into the furnace pump?

An exterior condensate drain line will absolutely freeze in the Rhode Island winter. I’ve visited Rhode Island in the winter and respect how cold it gets!

You should be able to route the dehumidifier drain line to condensate pump that serves the central air handler. Don’t connect the line with a Tee fitting to avoid backups and air pressure differentials. Better to route the dehumidifier drain line directly to the pump. Route the new line downward so it gravity drains to the pump.

A float switch operates the condensate pump when the reservoir fills to normally full level. My condensate pump has two inlet openings in the top for two condensate drain lines: One tube for the Aprilaire humidifier which runs in the winter with the furnace; and a 2nd tube for the AC evaporator coils which runs in the summer. The pump therefore operates during the heating and cooling seasons.

Hi, I hope you can help us figure this out. We have a dehumidifier that works very well when sitting on the floor in the basement. We want to run the drain line to the washing machine output, so mounted the dehumidifier on a shelf about five feet off the floor. It ran all night without collecting any water. Is there a known issue with mounting them high? If so, what’s the recommended height? I see that yours is not on the floor, so I have hope that this can be resolved. Thanks

Is the condensate bucket in the machine? The condensate bucket must be in the machine at all times – even if connected to a drain line – because the bucket closes a flood safety switch. The machine won’t run if the bucket is missing.